Individuals born with lower limb loss or those who have acquired such an amputation through injury, infection, or disease are traditionally fit with a prosthetic socket and limb so as to provide them with the opportunity to achieve independent ambulation. In order for a patient to successfully stand and ambulate with a prosthesis, the prosthetic socket must transfer the loads that are normally distributed through the skeletal system to the residual limb and its delicate soft tissues. A prosthetic socket must have an intimate fit with the residual limb in order to effectively and safely transfer these forces. However, no socket fit is perfect and residual limbs continually change shape over time as the residual limb matures and/or atrophies, which may occur over the course of the day, week, or month. Further, patients often experience daily fluctuations in residual limb volume that occur as fluid enters and leaves the residual limb.
Patients are often encouraged to use removable interface materials to accommodate the changing size of the residual limb and maintain an optimal fit. Those whose limbs change in volume during the day are commonly advised by their practitioners to add or remove prosthetic socks in order to effectively manage these changes. A practitioner might recommend that certain numbers and/or plies (i.e., thickness) of socks be added or removed at certain times of the day, before or after certain activities or other treatments (e.g., dialysis), or when discomfort or pain is experienced by the patient, depending on the presentation of the residual limb tissues and the nature of discomfort experienced.
Changing socks properly promotes healthy skin tissues by maintaining well-distributed pressures and shear stresses on the residual limb and encourages a stable gait by limiting the pistoning (i.e., rubbing between the limb and socket) of the prosthesis on the residual limb. However, frequent donning and doffing of the prosthesis is inconvenient and many patients may elect not to add or remove socks. Further, individuals with cognitive impairments or poor limb sensation often have difficulty choosing or determining when to make sock changes. Further yet, many patients often fail to remember to conduct prescribed sock changes and, even when they do remember to conduct prescribed sock changes, fail to document such sock changes. The documenting of sock changes provides important diagnostic information to the practitioner.
If residual limb volume is not properly accommodated through volume management strategies such as prosthetic sock use, then residual limb soft tissues may be put at risk for edema, breakdown, or other skin conditions, such as verrucous hyperplasia. These factors are believed to ultimately contribute to dissatisfaction, discomfort, inactivity, disuse/abandonment of the prosthesis, and/or infections that may, in extreme cases, require surgical intervention or re-amputation of a portion of the limb. Although the exact cause is not known, the incidence of skin breakdown ranges from 24% to 41%, suggesting it is a serious problem for many amputees.
A first barrier to progress in the prescription and clinical application of sock accommodation strategies is a scarcity of data from which to derive meaningful decisions and recommendations concerning sock usage. Existing techniques do not indicate if and how consistently amputee patients change socks to address volume management issues and, further, if changing socks improves users' comfort and satisfaction with the prosthesis. The root of the difficulty in obtaining such data is a technological one: no instrument exists for monitoring sock use, or for facilitating implementation of volume accommodation prescriptions.
A second barrier to reaching these goals is the absence of normative data. In order to derive meaningful clinical knowledge from the application of novel therapeutic solutions, observation and study of the target population under usual and customary circumstances is required. However, again, no instruments currently exist for observing and studying a target population under usual and customary circumstances with respect to sock usage.
A third barrier to reaching these goals is the meaningful translation of such knowledge into clinical practice. Since no instruments currently exist for observing and studying a target population with respect to sock usage, it follows that techniques have yet to be considered, much less developed, for exploiting such data.
Attempts to obtain and provide practitioners with information about prosthetic patients' participation in their free-living environments has resulted in the development of accelerometer-based monitoring devices and strain-gage monitoring devices that are intended to be worn on the patient or attached to a prosthesis.
Accelerometer-based devices have been used to measure “activity” by means of step counts. The information collected with accelerometer-based devices is collected perpetually, stored locally (i.e., on the unit), and then retrieved at a later date. A classification accuracy of 98% has been considered acceptable for accelerometer-based activity monitors described in the literature. They require limited power and measure steps across a range of walking speeds. However, step counts provide limited clinical information as to how the prosthesis is used or how the user manages limb volume change. Thus, prosthetic interventions designed to help manage limb volume change would be expected to show similar results to studies reported in the literature that have evaluated componentry designed to alter loading patterns (such as shock-absorbing pylons or microprocessor-controlled prosthetic knees). These studies have reported that there is no measured clinical effect to changes in interventions when step counts are used as an outcome. Further, as step monitors are sensitive, stand-alone devices, they must be properly oriented on the patient to collect accurate data, and they can be selectively removed by the patient. Failure to wear the device properly or regularly may result in incomplete or erroneous usage information.
Strain gage-based devices exist to measure prosthesis forces and might help provide insight into how the prosthesis is used, but current devices are limited to short term use (e.g., 7 hours). Thus, the existing solutions to collecting perpetual, clinically-relevant information in free-living environments are limited in their capability to measure characteristics of clinical interest to a rehabilitation team. Existing solutions do not align with the needs of an efficient practice and add to the overall time and expense of care provided.
Accordingly, existing techniques fail to indicate how prosthetic users should manage their volume fluctuations with prosthetic socks or how sock usage affects prosthetic fit and comfort. Existing techniques also fail to indicate whether individuals, in their daily lives, follow clinical recommendations for accommodation and whether compliance affects their health and comfort.